Some industrial processes call for the introduction of fluids into rotating tubes. In many such situations it is desirable, if not essential, that this be done without ambient matter becoming entrained with the fluid as it flows from a stationary conduit into the rotating tube.
For example, in constructing preforms from which optical fibers may be drawn, vapors of materials such as SiCl.sub.4, GeCl.sub.4, BCl.sub.3 and POCl.sub.3 are entrained in an oxidizing carrier gas such as oxygen. The vapor stream is then drawn through a stationary conduit and into a rotating glass preform tube. In order to inhibit the vapor stream from leaking to ambient atmosphere, and ambient air from entering and thereby contaminating the vapor stream, a rotary seal has been provided at the junction of the stationary and rotary tubes. This seal has been provided by locating an end portion of one of the tubes within an end portion of the other tube and positioning one or more resilient O-rings or washers between the two tubes. However, this arrangement has been less than satisfactory since at least one of the tubes is constantly rubbing against the resilient O-rings causing them to become heated and to wear out. Structural deterioration of the O-rings, of course, soon leads to leakage which is aggravated whenever, as here, there is a pressure differential between the fluid stream and ambient. Furthermore, in such highly controlled situations as optical fiber preform manufacture even a very slight leak can create severe problems. For example, a leak PPM to ambient surrundings can endanger personnel since the vapor stream is toxic. Such leakage also alters the rate of vapor stream flow into the preform which rate must be precisely controlled. Conversely, an ingress of ambient air will also alter the flow rate as well as contaminate the vapor stream with water vapor.
Thus, it is desirable to provide improved apparatuses for supplying a rotating tube with fluid uncontaminated with ambient air such as is done in fabricating optical fiber preforms. It is this task to which the present invention is primarily directed.
In one form of the invention a protective end member is provided for a rotatable tubular member. The protective end member has a housing formed with a bore therein of greater inside dimensions than the outside dimensions of the tubular member for receiving an end of the tubular member without making contact with it. Means are provided within the housing for permitting the introduction of fluid into the interior of the tubular member. Means are also provided within the housing for permitting the introduction of a purging fluid into the housing bore at a pressure in excess of ambient pressure to prevent contaminating materials from being introduced into the interior of the tubular member from the ambient atmosphere.
In another form of the invention apparatus is provided for supplying fluid to a rotary tube substantially uncontaminated with ambient air. The apparatus comprises an end cap having an open ended bore in which an end portion of the tube may be rotatably positioned. First conduit means extend into the end cap through which fluid may be fed into the rotary tube. Second conduit means communicate with the end cap bore through which a purge fluid may be fed into and at least partially through the bore to the exterior of the end cap.
In still another form of the invention apparatus is provided for inhibiting ambient air from entering an end of a rotatable tube into which a stream of fluid is to be delivered. The apparatus comprises an end cap adapted to be positioned closely about an end portion of the rotatable tube so as to form a generally annular channel therebetween which communicates with the exterior of the end cap. The end cap defines a first passage through which a first stream of fluid may flow into the rotatable tube and a second passage through which a second stream of fluid may flow into and through the annular channel to the exterior of the end cap.